Oxidative addition of RCO2H and HX to chiral diphosphine complexes of iridium(I):: Convenient synthesis of mononuclear halo-carboxylate iridium(III) complexes and cationic dinuclear triply halogen-bridged iridium(III) complexes and their catalytic performance in asymmetric hydrogenation of cyclic imines and 2-phenylquinoline

Mononuclear iridium(III) complexes of general formula IrX(H)(O2CR)[(S)-binap] (2, R = CH3; 3, R = Ph; 4, R = C6H4CH3-p; a, X = Cl; b, X = Br; c, X = 1) were prepared by one-pot reaction of [Ir(mu-X)(cod)12 with 2 equiv of (S)-BINAP [=2,2'-bis(diphenylphosphino)-1,1'-binaphthyl] and an excess of the corresponding carboxylic acid in toluene. The structure of (S)-2-4 bearing an (S)-BINAP was confirmed to be OC-6-23-A (Lambda-conformation) by X-ray analysis of (S)4a-c. In this reaction, the iridium(1) complex (I) {Ir(mu-Cl)[(S)-binap]}(2) [(S)-5a] and pentacoordinated iridium(l) complexes IrX(cod)[(S)-binap] [(S)-7b, X = Br; (S)-7c, X = I] were generated prior to the oxidative addition of carboxylic acid. Cationic inuclear iridium(III) complexes of general formula [{Ir(H)[(S)-binap]}(2) (mu-X)(3)]X [(S)-8: a, X = Cl; b, X = Br; c, X = 1] were prepared, and their cationic bifacial octahedral dinuclear structure was characterized by spectral data and combustion analysis. The anionic portion of these complexes could be replaced by NaPF6, leading to the corresponding PF6 salts [{Ir(H)[(S)-binap]}(2)(mu-X)(3)]PF6 [(S)-8: d, X = Cl; e, X = Br; f, X = I]. Iodo-acetate complexes of p-TolBINAP (=2,2'-bis(di-4-tolylphosphino)-1,1'-binaphthyl) [(S)-9c] and SYNPHOS [=2,2',3,3'-tetrahydro(5,5'-bi-1,4-benzodioxin)-6,6'-diyl]bis(diphenylphosphine)] [(S)40c] were also prepared according to the method used for the BINAP complex (S)-2c and were characterized spectroscopically. Cationic dinuclear complexes of p-TolBINAP [(S)-11c] and SYNPHOS [(S)-12c] were also generated. Using these complexes, the effect of halide variation was studied by asymmetric hydrogenation of 2-phenylpyrrolidine (13) and 2-phenyl-4,5,6,7-tetrahydro-3H-azepine (15) along with 2-phenylquinoline (16), and the results indicated that iodide complexes were better catalyst precursors for catalytic activity than the corresponding chloride and bromide complexes, but were not superior in enantioselectivity.